Generally, wiper blades are used to remove rainwater falling on a windshield of a car to ensure clear visibility. Further, wiper blades are also used to wipe off dirt stuck on the car windshield. Recently, there has been introduced in the art a wiper blade including a straight frame and a spoiler attached to the frame. The spoiler is designed to reduce resistance applied to the wiper blade while the car is traveling.
Explanation will be made hereinafter as to one example of prior art wiper blades with reference to FIGS. 1 and 2.
FIG. 1 is a perspective view showing a prior art wiper blade. FIG. 2 is a sectional view taken along the line A-A of the wiper blade shown in FIG. 1.
As shown in FIGS. 1 and 2, the prior art wiper blade includes the following: an adapter 10 for coupling to a wiper arm; a straight frame 30 joined with the adaptor; a spoiler 20 located on the frame 30; a wiper lip 40 coupled to the frame 30 and extending downwardly from the frame 30; and a tip clamp 50 for clamping ends of the spoiler 20 and the frame 30.
The frame 30 includes an elongated metallic plate. The spoiler 20 has an approximately triangular cross-section with an open bottom side, wherein the frame 30 can be fitted to the bottom side. A slit 34 for fixing the wiper lip 40 is formed at a midway portion of the frame 30 in a longitudinal direction of the frame. The wiper lip 40 includes a head 41, a body 42 and a contactor 43. The head is fitted to the spoiler 20 through the slit 34 of the frame 30 and fixed to the frame 30. The body 42 is caught on the lower portion of the frame 30. The contactor contacts a windshield.
FIG. 3 is a perspective view showing when the spoiler of the prior art wiper blade is placed on a windshield. FIG. 4 shows simulations on the air flows passing by the spoiler when the spoiler of the wiper blade is placed as shown in FIG. 3 and a vehicle travels at a velocity of 100 km/h. In FIG. 4, an a area shows that the flow velocity of the air is equal to or more than 290 km/h, a b area shows that the flow velocity of the air is less than 290 km/h and equal to or more than 230 km/h, a c area shows that the flow velocity of the air is less than 230 km/h and equal to or more than 170 km/h, and a d area shows that the flow velocity of the air is less than 170 km/h and equal to or more than 110 km/h.
As shown in FIG. 3, the windshield 1 is inclined relative to the horizontal plane (i.e., X-Z plane). The flow velocity of the air flowing horizontally increases as the air flows along the vehicle. Further, the flow velocity of the air increases more as the air flows along the inclined windshield. Such an increase in the flow velocity of the air may be explained with a Venturi effect based on Bernoulli's Principle or a Kutta Condition (Coanda Effect). The air flow flowing along the surface of the vehicle was simulated using a finite element program. When the spoiler 20 of the wiper blade is placed on the windshield as shown in FIG. 3 and the vehicle travels at a velocity of 100 km/h, the air flow flowing along the surface of the vehicle is as shown in FIG. 4.
According to the simulation results shown in FIG. 4, when the vehicle equipped with the spoiler 20 of the prior art wiper blade travels at a velocity of 100 km/h, the velocity of the air, which horizontally proceeds from the front of the vehicle, gradually increases up to 170 km/h as the air passes by the surface of the vehicle. Further, the flow velocity of the air sharply increases as the air passes by the spoiler 20. Furthermore, the air flows by an end of the windshield 1 at a velocity of 300 km/h or more and then flows by a roof of the vehicle at a velocity of 320 km/h or more.
Table 1 provided below shows the values of the aerodynamic forces acting on the spoiler 20 depending upon the aforesaid air flows.
TABLE 1AverageMinimumMaximumUnitValuevaluevaluevalueResultant force[N]40.5246515840.341240.084740.5247X-directional force[N]0.0180934130.01805340.01799210.018105Y-directional force[N]−13.78663257−13.7255−13.7866−13.6399Z-directional force[N]−38.10742475−37.9344−38.1074−37.6927
According to Table 1, when the vehicle travels at 100 km/h, a rearward force of 38.1N is generated in the wiper blade in a horizontal direction (negative Z-direction) and a downward force of 13.7N is generated in the wiper blade in a vertical direction (negative Y-direction). An aerodynamic force in a longitudinal direction (X-direction) approximates to nearly zero. A resultant aerodynamic force from a resultant force of those aerodynamic forces comes to about 40.52N. The above-mentioned increase in the aerodynamic forces may apply a great force to the arm to which the wiper blade is attached. The large aerodynamic force is problematic since it causes a fatigue load and the deformation of the wiper blade while the vehicle is traveling and deteriorates the durability of the arm.
Further, the large aerodynamic force is also problematic since it can deform the spoiler of the wiper blade, which is composed of an elastic material and has an empty inside space, while the vehicle is traveling.
Furthermore, the large aerodynamic force during traveling of the vehicle may change the shape of the spoiler. If the shape of the spoiler is not maintained, then the aerodynamic characteristics change, and thus, the aerodynamic forces applied to the wiper blade can vary. This may cause the wiper blade to conduct irregular wiping operations.